The present invention relates, generally, to a drilling apparatus and method for drilling a well. More particularly, but not by way of limitation, the present invention relates to a non-reactive torque device that contains an inner bit and a counter-rotating outer bit and a related method of use. Embodiments of the present invention will significantly reduce the reactive torque generated during the drilling phase of a well bore.
In the search for oil and gas, operators have utilized various types of devices to drill wells. Operators are continually searching for ways to drill the wells faster and more economically. Traditionally, a specifically designed drill string was used to drill wells. The drill string would have attached thereto a drill bit. To drill the well, the driller would cause the drill string to rotate, which would in turn cause the bit to rotate, and thus, drill the well. Over the years, various types of drill strings have been developed in order to enable drilling directional, or inclined, well bores.
Further, different types of bottom hole assemblies have also been developed to facilitate drilling these wells. A typical directional drill string may contain a bottom hole assembly which includes: a bit, a bent sub, a drilling motor, and one or more measurement-while-drilling surveying and logging tools. When using this type of bottom hole assembly, the drill string ideally is held stationary with respect to down hole rotation. The drilling motor causes rotation of the bit via circulation of drilling fluid through the drilling motor, as is well understood by those of ordinary skill in the art. With the drill string held stationary with respect to rotation, the well is drilled in the desired, controlled direction of the bend in the bent sub.
A common problem encountered when using this type of drilling assembly is the torque generated by the bit. Torque from the bit torque generates an equal and opposite reactive torque that is transferred from the motor into the bottom hole assembly and drill string, causing it to counter-rotate relative to the bit. Further, the reactive torque, and hence the drill sting counter-rotation, varies due to drilling conditions, such as the weight applied to the bit, properties of the rock being drilled, and hole condition, all of which vary independently of each other. As the bent sub is part of the bottom hole assembly being counter-rotated, the direction in which the well is drilled changes with the changes in reactive torque.
As a result, the directional driller is required to make numerous surface adjustments of the drill string, and hence the bent sub, to maintain drilling in the desired direction. These numerous adjustments cost valuable rig time and reduce the efficiency of the drilling operation. By eliminating, or greatly reducing, the reactive torque in the bottom hole assembly and drill string, drilling can proceed unabated in the desired direction, saving valuable rig time. Other benefits of eliminating, or reducing, reactive torque include the ability to use more powerful motors and more weight on the bit to increase drilling rates and enable drilling of a smoother, less tortuous borehole for running logging tools and setting casing. A non-reactive bit apparatus and method were disclosed in U.S. Pat. No. 5,845,721 entitled “Drilling Device And Method Of Drilling Wells”, which is incorporated herein by express reference.
As those of ordinary skill in the art will appreciate, daily rig costs are substantial. In many cases, after a well is drilled, the well is prepared for running and cementing a casing string into the well. Hence, any time saved cleaning, running, and cementing the casing provides significant cost savings. Prior art tools have not enabled an operator to effectively drill with a casing string forming a part of the work string due to structural limitations of the casing string and the casing string thread connections.
The casing strings and casing string connections are not structurally designed to handle the stress and strain applied by the numerous torquing requirements for a drill string. However, embodiments of the non-reactive torque drilling device herein described, drilling with an attached casing string is possible. Numerous advantages and features flow from embodiments of the present invention.
Therefore, there is a need for a drilling apparatus that will allow the drilling of a well with a casing string attached thereto. There is also a need for a non-reactive drilling tool with dual bits, that enables a casing string to be left within the well after cessation of drilling operations. The casing string can be cemented in place, and other remedial well work can then be performed, such as perforating the casing to produce hydrocarbons from a subterranean reservoir.